1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device and, more particularly, to a manufacturing method for a semiconductor device provided with a capacitor on an interlayer dielectric, the capacitor comprising a silicon nitride film serving as a capacitor dielectric film.
2. Description of Related Art
In recent years, semiconductor memory devices employ silicon nitride films as capacitor dielectric films in order to increase capacitance of capacitors. In order to take full advantage of using silicon nitride films, a process for forming a silicon nitride film is sometimes employed, wherein a lower electrode composed of a silicon type material, typically a polycrystalline silicon material, is first formed on an interlayer dielectric, then this specimen is placed in a deposition chamber to be subjected to pretreatment in which the specimen is subjected to heat in an ammonia gas atmosphere in the deposition chamber, the pressure of which has been reduced (this pretreatment will be hereinafter referred to as "in-situ surface nitriding (ISN)"). Then, an ammonia gas and a gas for forming a silicon type thin film are introduced into the deposition chamber to form a silicon nitride film on the lower electrode and the interlayer dielectric. The reduced pressure CVD method is employed as a typical method for forming the silicon nitride film after the ISN treatment is finished.
A native oxide produced on the lower electrode is reduced and thermally nitrided during the ISN treatment. Thus, a silicon nitride film by the ISN is formed on a surface of the lower electrode. This provides an advantage in that a chance for an oxide film to be produced between the lower electrode and the silicon nitride film produced by the CVD method is minimized, permitting an advantage of using the silicon nitride film as a capacitor dielectric film to be easily obtained.
Generally, in the process mentioned above, a heat treatment known as "healing oxidation" is carried out on the silicon nitride film, which has been formed, so as primarily to repair defects or the like of the film.
However, according to experiments performed by the inventors of the present application have revealed that a portion of the silicon nitride film that is formed on the interlayer dielectric tends to be thinner than another portion that is formed on the lower electrode in the foregoing process including the ISN treatment. It has also been found that the thickness is considerably influenced by the degree of vacuum in a deposition chamber in the ISN treatment.